Quadrasonic sound system for two channel transmission

ABSTRACT

A signal transmission system comprising microphones for obtaining 4-channel signals by collecting sounds produced in a sound source room, an encoder for producing 2-channel signals by combining the 4- channel signals with such a phase relationship as prevents them from offsetting each other, means for transmitting said 2-channel signals, a decoder for producing 4channel signals by combining said 2-channel signals with such a phase relationship as prevents them from offsetting each other so as to form signals representing the sum and balance or difference of said 2-channel signals, and speakers for reproducing sounds from 4-channel signals reproduced in the decoder.

United States Patent 11 1 Itoh et al.

[ Jan. 22, 1974 [54] QUADRASONIC SOUND SYSTEM FOR TWO 3,632,886 1/1972 Scheiber 179/1 G CHANNEL TRANSMISSION OTHER PUBLICATIONS [75] $12 "f" Tmhiaki Four Channels and Compatibility by Scheiber Audio 0 0 apan Engineering Society Preprint, Oct. 12-15, 1970. Assigneei Sallslli Electric -9 Tokyo, Multichannel Stereo Matrix Systems An Overview Japan Audio Engineering Society, July/August 1971. [22] Filed: Feb. 1, 1972 P E K h] H Cl if rimary xaminer at een a y [21] 16 11 .2 55 54! Ez iTh o leeQii ieq one Attorney, Agent, or Firm-Harris, Kern, Wallen & [30] Foreign Application Priority Data Tinsley Feb. 5, 1971 Japan 46-4440 Sept. 1, 1971 Japan 46-79136 [57] ABSTRACT Sept. 1, 1971 Japan 46-79137 A Signal transmission System comprising microphones for obtaining 4-channel signals by collecting sounds [52] us. Cl "179/1 P oduced in a sound source room, an encoder for pro- [51 I t H045/00 i ewh als tls n linine t e 412 1 11 1?! d G ET I signals with such a phase relationship as prevents them 0 can H00 4 6 1 from offsetting each other, means for transmitting said Z-channel signals, a decoder for producing 4-channel signals by combining said 2-channe1 signals with such [56] References Cited a phase relationship as prevents them from offsetting UNITED STATES PATENTS each other so as to form signals representing the sum 3,745,252 7/1973 aue 4 179/l 00 and balance or difference of said 2-channel signals, 3 2/1973 Berkovm and speakers for reproducing sounds from 4-channe1 3,708,631 l/l973 Bauer h d 3,684,835 8/1972 Orban 179/1 00 slgnals reproduced m t e ecoder 30 Claims, 9 Drawing Figures FL O---u-1'PHASE SHIFTER f I L I 3 ADDER 2 1 l8 12L PHASE SHIF'TER W21 /4 gvuzz PHASE SHIFTER I7 .121? i 12 I9 5 ADDER FR O PHASE SHIFTER PATENTEU JAN 2 918:"?

sum 2 0F PHASE 5H|I=TER NI PATENTEUJAHZZi-SF SHEET 3 OF 6 oooom oqm QUADRASONIC SOUND SYSTEM FOR TWO CHANNEL TRANSMISSION This invention relates to a signal transmission system used in, for example, broadcasting, storing musical tones in phonographic records and reproducing them therefrom, recording data in a tape recorder and reproducing them therefrom and wire or wireless signal transmission, wherein multichannel signals are transmitted or recorded in a form converted to those of fewer channels and the signals of said fewer channels are reproduced in a form converted back to those of multichannels.

In recent stereophonic sound reproduction, it is contemplated to adopt a system of collecting sounds to form 4-channel signals, transmitting them in a form converted to Z-channel signals and after reception, reproducing said 2-channel signals in a form converted back to 4-channel signals. Namely, there are arranged microphones MFL, MFR, MRL and MRR, for example, at the four corners of a sound source room to collect sounds, thereby obtaining 4-channel signals FL, FR, RL and RR. The 4-channel signals are converted into 2-channel signals L, and R, including 4-channel signal component as follows:

The above-mentioned signals AFR, ARR, AFL and ARL are signals proportionate to said 4-channel signals FL, FR, RL and RR and the mark A denotes a value chosen within the range of A l. The 2-channel signals L, and R, are conducted to a receiver or decoder through two channels such as broadcasting channels, phonographic records, magnetic tapes, etc. The Z-channel signals conducted to a decoder, are converted to the following 4-channel signals:

nals proportionate to the 2-channel signals L, and R,. Sum signals FL and FR, correspond to direct sounds immediately brought to the hearers cars from the sound sources arranged at the front part of a sound source room. The difference signals RL and RR, correspond to indirect sounds reaching the hearers ears from all directions after being reflected by the walls and ceiling of the sound source room. The 4- channel signals FL FR RL, and RR; are conducted for stereophonic reproduction to the speakers SFL, SFR, SRL and SRR disposed at the four corners of a sound reproduction room in corresponding relationship to the microphones MFL, MFR, MRL and MRR set in the sound source room.

However, the aforementioned signal converting system from 4 to 2 sum-difference type which simply adds up signals or deducts them from each other. Where, therefore, there are formed in an encoder Z-channel signals L, and R, composed as shown in the aforesaid equation 1, sound signals located at the substantially middle point between the microphones MFL and MRL are extinguished in the encoder, as seen from said equation, failing to be reproduced in the listening then sound signals located at the middle point between the microphones MFR and MRR are attenuated in the encoder, as apparent from the equation 3 above, failing to retain the orginal sound location when reproduced. Where four inputs having the same phase and level are simultaneously supplied to four microphones MFL, MFR, MRL and MRR respectively, they cannot be transmitted or recorded under normal condition, failing to be properly reproduced.

It is accordingly an object of this invention to provide a signal transmission system capable of unfailingly transmitting or recording signals representing sounds produced anywhere in a sound source room, particularly sounds located at the middle point of any two adjacent input channels without either attenuation or extinction.

Another object of the invention is to provide a signal transmission or recording system capable of transmitting or recording a signal of each channel under good condition even where all input channels are supplied with the same input at the same time.

According to the invention, there is provided a signal transmission system comprising means for obtaining multichannel signals by collecting sounds produced in a sound room, means for combining the multichannel signals with a prescribed amplitude and phase relationship to form signals of fewer channel, said phase relationship preventing them from offsetting each other; means for transmitting said signals of fewer channels; and means for combining said signals of fewer channels with a prescribed amplitude and phase relationship to convert them back to those of multichannels wherein conversion of signals of fewer channels back to those of multichannels can be effected without either attenuation or extinction of signals thus converted.

This invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. I is a block diagram of a signal transmission system according to an embodiment of this invention;

FIG. 2 is a schematic circuit diagram of an encoder used in the embodiment of FIG. 1;

FIG. 3 shows a concrete circuit arrangement of a phase shifter used in the encoder of FIG. 2;

FIG. 4 is a curve diagram showing the phase shifting property of the phase shifters of FIG. 3;

FIG. 5 is a circuit diagram of a decoder used in the embodiment of FIG. 1;

FIG. 6 is a curve diagram showing the phase shifting property of phase shifters used in said decoder;

FIG. 7 is a block diagram of a signal transmission systqma ewqinstq mbe mbpimsatgf th t y ntiqn;

FIG. 8 is a circuit diagram of the encoder used in the m dimen QL 7 n FIG. 9 is a circuit diagram of another type of encoder used in the embodiment of FIG. 7.

As illustrated in FIG. 1, there are arranged in a sound source room 1 four microphones MFL, MFR, MRL and MRR in four places, for example, that is, on the front left and right sides and on the rear left and right sides respectively to obtain directional 4-channel audio input singals FL, FR, RL and RR. These 4-channel signals FL, FR, RL and RR are conducted to an encoder 2 to be combined with a predetermined amplitude and phase relationship for conversion to Z-channel signals L, and R, composed as follows:

L, FL AFR +jRL +jARR R, FR AFL jRR jARL 4 The notations +jRL and +jARR, show signals obtained by advancing the phase of the signals RL and ARR by 90, for example, with respect to the other signals, FL and AFR which are phase shifted by a reference angle. The notations ]RR and jARl indicated signals obtained by delaying the phases of the signals RR and ARL with respect to the other signals FR and AFL which are phase shifted a reference angle. It should be noted that in the equations 4, only the relative phase shift amounts between the four signals FL, FR, RL and RR are presented. The reference phase shifts do not appear in the equations 4. The 2-channel signals L, and R, drawn out of the encoder 2 are conducted to 2-channel paths 3 and 4 respectively. The 2- channel system which couples the output signals L, and R, from the encoder 2 to a decoder 5 may consist of a broadcasting system, or a recording medium such as a stereo phonographic record or magnetic tape. The 2- channel signals L, and R, carried through the 2- channel system are combined in a decoder 5 with a predetermined amplitude and phase relationship for conversion to the directional 4-channel signals audio output FL,, FR,, RL, and RR, composed as follows:

The mark A indicated in the aforesaid equations 4 and 5 may have differnet values between the encoder and decoder. Further, the marks A prefixed to FL, FR, RL and RR may have different values. The notations FL, and FR, represent sum signals directly brought to the hearers ears, and the notations RL, and RR, denote difference, signals indirectly reaching the hearers ears. Output signals FL,, FR,, RL, and RR, from the decoder 5 are conducted for stereophonic reproduction, typically through power amplifiers (not shown), to the speakers SFL, SFR, SRL and SRR arranged in a reproduction room in corresponding relationship to the microphones MFL, MFR, MRL and MRR disposed in the sound source room.

According to the foregoing embodiment, some signal components constituting output signals L, and R, in the encoder 2 are advanced or delayed 90 in phase with respect to the other signl components as seen from the aforesaid equation 4, thus preventing signals representing sounds located at the middle point of two adjacent microphones or input channels from being attenuated or extinguished. This has the effect of enabling the same kind of input to be always transmitted or recorded under good condition even when they are supplied to all the channels at the same time.

There will now be described by reference to FIG. 2 an encoder 2 used in an embodiment of this invention. The encoder 2 comprises phase shifters l2 and 15 supplied with signals FL and FR representing the sounds collected at the front part of a sound source room 1, phase shifters l3 and 14 supplied with singals RL and RR representing the sounds collected at the rear part of the sound source room 1, a variable attenuator VR, connected between the input terminals of the phase shifters 13 and 14 and formed of a variable resistor, another variable attenuator VR, connected between the output terminals of the phase shifters Hand 15 and formed of a variable resistor, an adder 16 connected to the output terminals of the phase shifters l2 and 13, and another adder 17 connected to the output terminals of the phase shifters l4 and 15. From the output terminals 18 and of the adders l6 and 17 are drawn out the signals L, and R, respectively. The phase shifters l2 and 15 have the same phase shifting characteristics to phase shift an input signal by a reference angle, the phase shifter 13 has such a phase shifting characteristic as phase shifts an input signal by a sum of the reference angle and plus and the phase shifter 14 has such a phase shifting characteristic as phase shifts an input signal by a sum of the reference angle and minus 90.

The signal FL is drawn out as such at the output terminal 18 through the phase shifter 12 and mixer 16 and also as AFL at the output terminal 19 through the phase shifter 12, variable attenuator VR, and adder 17. The signal RL is drawn out as +jRL at the output terminal 18 through the phase shifter 13 and adder l6 and also as jARL at the output terminal 19 through the variable attenuator VR,, phase shifter 14 and adder 17. The signal RR is drawn out as +jARR at the output terminal 18 through the variable attenuator VR,, phase shifter 13 and adder 16 and also as RR at the output terminal 19 through the phase shifter 24 and adder 17. The signal FR is drawn out as AFR at the output terminal 18 through the phase shifter 15, variable attenuator VR, and adder l6 and also as FR at the output terminal 19 through the phase shifter 15 and adder 17. Accordingly, there are formed by the encoder 2 the Z-channel signals L, and R, composed as shown in the equation 4 from the 4-cl1annel signals FL, FR, RL and RR.

The variable attenuator VR, may be connected between the input terminals of the phase shifters 12 and 15. Further, the foregoing description refers to the case where the phase shifters l2 and 15 had the same phase shifting characteristics and the phase shifters l3 and 14 had such a phase shifting characteristic as advanced or delayed the signals received therein 90 from those supplied to the first mentioned phase shifters l2 and 15. If, however, the front signals FL and FR representing the sounds collected at the front left and right sides of a sound source room are displaced in phase within less than 90, then these signals will not counterbalance each other. Therefore, one of the phase shifters 12 and 15 may carry out phase shifting within the range of from 45 with respect to the other to +45". Where the phase shifters l2 and 15 conduct phase shifting independently of each other, the aforementioned range of phase shifting is so chosen as to prevent the mutual phase displacement of output signals from said phase shifters l2 and from exceeding 90 at maximum. In contrast, where the rear signals RL and RR representing the sounds collected at the reat left and right sides of the sound source room 1 are displaced about 90 in phase with respect to the front signals, then these signals will not fully counterbalance the front signals. Accordingly, the phase shifter 13 may perform phase shifting within the range of from 45 to 135 and the phase shifter 14 within that of from 45 to --l 35with respect to at least one of the phase shifters l2 and 15. Where the phase shifters l3 and 14 carry out phase shifting independently of each other, these ranges of phase shifting are so chosen as to prevent the mutual phase displacement of output signals from said phase shifters l3 and 14 from decreasing from 90 at minimum.

There will now be described by reference to FIGS. 3 and 4 the concrete circuit arrangement of a phase shifter used in the encoder 2. The phase shifter consists of a plurality of phase shifter units. One type of the phase shifter units is, for example, connected to the input terminal 21 of the phase shifter 12 of FIG. 3, and includes as indicated by 22, an NPN type transistor 31, to the collector electrode of which there is connected a capacitor 32 and to the emitter electrode of which there is connected a resistor 33. The other type of the phase shifter units is, for example, connected to the input terminal 23 of the phase shifter 15 and includes, as indicated by 24, an NPN type transistor 34, to the collector electrode of which there is connected a resistor 35 and to the emitter contact of which there is connected a capacitor 36. These phase shifter units shift the phase of output signals with the increasing frequency with respect to input signals supplied thereto. The phase shifters 12 to [5 shift, as illustrated in FIG. 4, the phase of outputs therefrom with respect to input signals supplied thereto over the range of audible frequencies due to phase shifter units being connected in series. If, in this case, the values of the capacitor and resistor of each phase shifter unit is properly chosen to obtain such initial value of phase shifting with respect to the frequency that, asshown in FIG. 4, the phase shifters I2 and 15 have the same phase shifting characteristic and the phase shifters 13 and 14 have such different phase shifting characteristics as cause output signals thereof to be displaced :90 from those of the phase shifters l2 and 15, then output signals of said phase shifters 12 to 15 will be progressively shifted in phase, as shown in FIG. 4, as input signals supplied thereto increase in frequency, with the original phase displacement kept unchanged between the output signals of phase shifters l2 and 15 and those of the other phase shifters l3 and 14.

There will now be described by reference to FIGS. 5 and 6 the circuit arrangement of a decoder 5. The decoder 5 comprises the known phase splitters, 41 and 42 each capable of producing output of the same phase as well as of inverted phase, and phase shifters 43 to 46, variable attenuators 47 to 49 and resistors 50 to 53, thereby obtaining output signals RL, and RR,. The phase shifter 44 producing output signals RL, has a reverse phase shifting characteristic to that of the shifter 13 supplied with output signals RL in the encoder 2 and the phase shifter 45 also has that to that of the phase shifter 14 supplied with input signals RR in encoder 2. Namely, as illustrated in FIG. 6, the phase shifter 44 delays its output in phase and the phase shifter 45 advances its output 90 in phase with respect to outputs of phase shifters 43 and 46 over the entire audible frequency range. The signal L, thus transmitted is drawn out as such at an output terminal 54 through the same phase signal output terminal of the phase splitter 41, resistor 50 and phase shifter 43, as jL, at an output terminal 55 through the same phase signal output terminal of said phase splitter 41, resistor 52 and phase shifter 44, as -(+jAL,) at an output terminal 56 through the reverse phase signal output terminal of said phase splitter 41, variable attenuator 49 and phase shifter 45, and as AL, at an output terminal 57 through the same phase signal output terminal of said phase splitter 41, resistor 50, variable attenuator 48 and phase shifter 46. The signal R, is drawn out as AR, at the output terminal 54 through the same phase signal output terminal of the phase splitter 42, resistor 53, variable attenuator 48 and phase shifter 43, as jAR) at the output terminal 55 through the reverse phase signal output terminal of the phase splitter 42, variable attenuator 47, and phase shifter 44, as +jR, at the output terminal 56 through the same phase signal output terminal of the phase splitter 42, resistor 51 and phase shifter 45, and as R at the output terminal 57 through the same phase signal output terminal of the phase splitter 42, resistor 53 and phase shifter 46. Thus from the output terminals 54, 55, 56 and 57 of the decoder 5 are obtained 4 channel output signals FL RL,, RR and FR -composed as shown in the equation 5 respectively. As described concerning the encoder 2, the phase shifters 43 and 46 may carry out phase shifting within the range of from 45 to +45", and the phase shifters 45 and 44 may perform phase shifting within the range of from 45 to and 45 to 135 respectively. With the decoder 5 there is more detailed description in U.S. Pat. Application Ser. No. 144,550 now U.S. Pat. No. 3,757,047 filed May 18, 1971.

There will now be described by reference to FIG. 7 another embodiment of this invention. Throughout the following description, the same parts are denoted by the same numbers and description thereof is omitted. According to this embodiment, there are provided in addition to the microphones MFL, MFR, MRL and MRR disposed at the four corners of the sound source room 1 new microphones MCL and MCR at intermediate locations between the front and rear microphones, that is, at middle points between MFL and MRL and between MFR and MRR to conduct 6-channel signals, namely, 4-channel signals FL, FR, RL, and RR and center-channel signals CL and CR to an encoder 61. These six channels are combined with a predetermined amplitude and phase relationship for conversion to 2- channel signals L and R composed as follows:

L FL AFR +jRL +jARR CL R,,=FR+AFLjRR-ARL+CR (6) The encoder 61 supplies, as shown in FIG. 8, signals FL, FR, RL, RR, CL and CR from the aforementioned microphones MFL, MFR, MRL, MRR, MCL and MCR to the phase shifters l2, l5, l3, 14, 62 and 63 respectively. The phase shifters 62 and 63 produce outputs having the same phase as those of the phase shifters l2 and 15. To an adder 64 are supplied output signal L, from an adder l6 composed as shown in the equation 4 and a signal CL drawn out of the left center channel microphone MCL through the phase shifter 62. These signals L and CL are mixed to produce at an output terminal 66 a signal L composed as shown in the equation 6 above. Further to an adder 65 are conducted output signal R, from an adder 17 composed as shown in the equation 4 and a signal CR drawn out of the right center channel microphone MCR through the phase shifter 63. These signals R, and CR are mixed to produce at an output terminal 67 a signal R composed as indicated in the equation 6. Further, output signals CL and CR from the center channelmicrophones MCL and MCR may be directly supplied to the adders 64 and 65 without passing through the phase shifters. The shifting angle in the phase shifters 62 and 63 may be changed within the range 'of 45 to 45.

The above-mentioned Z-channel signals L and R are transmitted to be combined in the decoder 5 having the same arrangement as shown in FIG. 5 with a predetermined amplitude and phase relationship, thereby otaining 4-channel signals FL,, FR,, RL, and RR composed as follows:

FL L, AR

The above output signals FL PR RL, and RR, from the decoder 5 are conducted for stereophonic reproduction to the speakers SFL, SFR, SRL and SRR arranged in corresponding relationship to the microphones MFL, MFR, MRL and MRR disposed at the four corners of the sound source room 1.

According to the embodiment of FIGS. 7 and 8, there are obtained in addition to at least 4-channel signals including the front Z-channel signals and the rear 2- channel signals another group of 2-channel signals from the microphones MCL and MCR disposed at the substantially middle part of the front and rear channel microphones, thus providing three channels on the left and right sides of the sound source room 1 respectively, with the resultant distinct separation between left and right channels. Since, as seen from the equation 7, output signals from the decoder 5 contain signals CL and CR just as they are obtained from the microphones MCL and MCR, there is least possibility that indirect sounds are extinguished due to internal loss of signals containing phase displaced components, even though sounds from the respective channels are blended, thereby offering the effect of obtaining substantially the same expansion of sounds as is realized in the original sound source room 1.

There will now be described by reference to FIG. 9 a modification of the encoder 61 of FIG. 8. Between the input terminals of the phase shifters l3 and 14 is disposed a switch 71 in series with the variable attenuator VR,, and between the output terminals of the phase shifters l2 and 15 is provided a switch 72 in series with the variable attenator VR,.

The changeover of the switches 71 and 72 permits conversion of the 6-channel signals FL, FR, RR, CL and CR to three groups of 2-channel signals L each composed as follows:

When the switches 24 and 26 are turned off, there results a condition similar to the case where there are removed the variable attenuators VR and VR, from the circuitry of the encoder 61, that is, the value of the prefix A attached to the signals received in the encoder 61 is reduced to zero. To the output terminal 73 of the encoder 61 is supplied the signal FL as such through the phase shifter 12 and adders l6 and 64, the signal R,, as +jRL through the phase shifter 13 and adders 16 and 64, the signal CL as such through the phase shifter 62. To the output terminal 74 of the encoder 61 is supplied the signal FR as such through the phase shifter 15 and adders l7 and 65, the signal RR as -jRR through the phase shifter 14 and adders l7 and 65 and the signal CR as such through the phase shifter 63 and adder 65. From the encoder 61, therefore, are obtained the 2- channel signals L and R composed as shown in the equation 8 above.

When the switch 71 is turned off and the switch 72 is turned on there are drawn out of the encoder 61 the Z-channel signals L and R composed as shown in the equation 9 above. When the switch 71 is turned on and the switch 72 is turned off, there are obtained from the encoder 61 the 2-channel signals L and R, composed as shown in the equation 10 above. Since these operations are apparent from the foregoing description, there is omitted detailed reference thereto.

When selectively obtained, the aforementioned three goups of Z-channel signals, that is, L R L R and L R are supplied to the decoder 5 of FIG. 5 through the two-channel system for conversion to the following three groups of 4-channel signals FL FR RL, and RR,,.

= FL(1 A) FR(2A), +j(RL ARR) CL ACR FR" R55 FR(l A FL(2A) 'j(RR ARL) CR ACL ob 11 5:: 31 ARM] j[FL(l A) +j(RL -ARR) CL ACR] +ji so sol +j[FR(1+ A) j(RR ARL) CR ACI 12) The adjustment desk of a studio is generally equipped with a pan pot for adjustment of blending, thereby permitting the free shift of the location of sound images or reproduced sounds. There, however, blending in the encoder overlaps that of said adjustment desk, difficulties arise depending on the type of program source. Moreover, where the encoder conducts a fixed blending, the elaborate shift of sound images by the adjustment desk will lose significance. Where, therefore, both switches 71 and 72 are turned off according to the modification of FIG. 9, then it is possible not only freely to shift the location of sound images using an external electric or acoustic blending element, for example, the aforementioned adjustment desk, but also to broaden the range of selecting the location of said sound images.

Further, the selective operation of the switches 71 and 72 permits the reproduction of the 4-channel sig nals composed as shown in the equations 11, 12 and 13 in a reproduction room, enabling sound images to be freely shifted. Accordingly, the modified encoder shown in FIG. 9 provides a sound effect more approaching that which is obtained in the sound source room, namely, induces the hearer to feel as if he were present in said sound source room itself.

Further, the switches 71 and 72 included in the encoder 61 of FIG. 9 may be disposed in series with the variable attenuators VR and VR in the embodiment of the encoder 2 shown in FIG. 2.

What we claim is:

I. An encoding method for use in a directional sound system wherein at least first, second, third and fourth directional sound signals are respectively coupled to first and second channels to produce first and second channel signals, and the first and second channel signals are decoded into at least four directional audio output signals which are coupled to at least four loudspeakers disposed around a listener in a listening room, said encoding method comprising the steps of:

combining said first sound signal at a larger amplitude level, said second sound signal at a smaller amplitude level, said third sound signal at a larger amplitude level, and said fourth sound signal at a smaller amplitude level in such a preselected phase relationship as said third sound signal and said fourth sound signal have substantially a plus 90 phase difference with respect to said first sound signal and said second sound signal, respectively, producing the first channel signal; and

combining said first sound signal at a smaller amplitude level, said second sound signal at a larger amplitude level, said third sound signal at a smaller amplitude level, and said fourth sound signal at a larger amplitude level in such a preselected phase relationship as said third sound signal and said fourth signal have substantially a minus 90 phase difference with respect to said first sound signal and second sound signal, respectively, producing the second channel signal.

2. A signal transmission system comprising:

first means for obtaining multichannel signals by picking up sounds produced in a sound room;

second means for connection to said first means for composing the multichannel signals into those of fewer channels by combining them;

third means for for transmitting said signals of fewer channels;

fourth means for connection to said third means for converting the signals of fewer channels to those of multichannels by combining them in preselected amplitude and phase relationships; and

fifth means for connection to said fourth means for reproducing sounds from the multichannel signals of said fourth means;

said first means comprising microphones MFL, MFR, MRL and MRR arranged on the front left and right sides and rear left and right sides of the sound source room so as to obtain four channel signals FL, FR, RL and RR respectively;

said second means comprising an encoder having first, second, third and fourth phase shifters connected to receive said signals FL, FR, RL and RR, said first and fourth phase shifters being connected to receive said signals FL and FR respectively so as to shift the phase of said signals FL and FR by a reference angle, and said second phase shifter being connected to receive said signal RL so as to advance the phase of said signal RL within the range of from 45 to 135 relative to output signals of said first and fourth phase shifters, and said third phase shifter being connected to receive said signal RR so as to delay the phase of said signal RR within the range of from -45 to -l35 relative to output signals of said first and fourth phase shifters,

a first variable attenuator connected between both input terminals of said second and third phase shifters,

a second variable attenuator connected between both output or both input terminals of said first and fourth phase shifters, said variable attenuators forming signals having amplitudes proportional to those of the signals supplied thereto with the proportional coefficient ranging within 0 to l including 0,

a first adder connected to the output terminals of said first and second phase shifters, and

a second adder connected between the output terminals of said third and fourth phase shifters, each of said adders producing one of said fewer channel signals as an output.

3. A system according to claim 2 wherein the output signals of said first and fourth phase shifters are of the same phase, the output signal from said second phase shifter has its phase advanced 90 from those of said first and fourth phase shifters, and the. output signal from said third phase shifter has its phase delayed from those of said first and fourth phase shifters.

4. A system according to claim 2 wherein said first means further comprises a microphone MCL disposed at the middle part of the microphones MFL and MRL placed at the front left side and rear left side of said sound source room respectively and another microphone MCR positioned at the middle of the microphones MFR and MRR located at the rear left side and rear right side of said sound source room respectively,

thereby forming 6-channel signals FL, FR, RL, RR. CL and CR; and

said encoder further includes a fifth phase shifter connected to receive said signal CL to shift the phase of an input by said reference angle, a sixth phase shifter connected to receive said signal CR to shift the phase of an input by said reference angle, a third adder connected to the output terminals of said fifth phase shifter and first adder to combine output signals therefrom, and a fourth adder con-. nected to the output terminals of said sixth phase shifter and second adder to combine output signals therefrom, each of said third and fourth adders producing one of said fewer channel signals as an output. 5. A system according to claim 4 wherein output signals from said fifthand sixth shifters have the same phase as those from first and fourth phase shifters.

6. A system according to claim 4 wherein there is connected a first switch in series with said first variable attenuator disposed between terminals of said second and third phase shifters and a second switch in series with said second variable attenuator disposed between terminals of said first and fourth phase shifters.

7. A system according to claim 10 wherein said fourth means comprises:

first and second phase splitters supplied with said fewer channel signals from said third means;

combining means connected to said phase splitters for combining output signals of said splitters; and

first, second, third and fourth phase shifters con nected to said combining means, the output signals from said first and fourth phase shifters being of the same phase, the output signal of said second phase shifter having its phase delayed 90 in phase with respect to those of said first and fourth phase shifters, and the output signal of said third phase shifter having its phase advanced 90 in phase with respect to those of said first'and fourth phase shifters.

8. An encoder system for use in a directional sound system wherein at least four directional audio input signals are respectively coupled to first and second channels to produce first and second channel signals, and the first and second channel signals are decoded into at least four directional audio output signals which are coupled to at least four loudspeakers disposed around a listener in a listening room, said encoder system comprising:

first means for coupling a first directional audio input signal at a larger amplitude level to the first channel with a first phase shift amount;

second means for coupling a second directional audio input signal at a larger amplitude level to the second channel substantially with said first phase shift amount;

third means for coupling a third directional audio input signal at a larger amplitude level to the first channel with a second phase shift amount;

fourth means for coupling a fourth directional audio input signal at a larger amplitude level to the second channel with a third phase shift amount;

fifth means for coupling said first and second directional audio input signals at smaller amplitude levles to the second and first channels substantially with said first phase shift amount, respeetively; and

sixth means for coupling said third and fourth directional audio input signals at smaller amplitude levels to the second and first channels with said third and second phase shift amounts, respectively;

said second and third phase shift amounts having differences of +45 to +135 and 45- to -l35, respectively, with respect to said first phase shift amount.

9. An encoder system according to claim 8 wherein said first to fourth means include first, second, third and fourth phase shifters, respectively, the phase shifting characteristics of said first and second phase shifters being substantially equal to each other, and the phase shift characteristics of said third and fourth phase shifters having differences of +45 to +1 35 and 45 to -l35, respecitvely, with respect to the phase shift characteristics of said first and second phase shifters.

10. An encoder system according to claim 8 wherein each of said fifth and sixth means includes resistor means.

11. An encoder system according to claim 10 wherein each of said resistor means of said fifth and sixth means includes a variable resistor.

12. An encoder system according to claim 10 wherein each of said fifth and sixth means includes a manually operable switch connected in series with said resistor means.

13. An encoder system according to claim 9 wherein said third and fourth phase shifters have phase shift characteristics of about -l and 90 differences with respect to those of said first and second phase shifters respectively.

14. An encoder system according to claim 8 includmg:

seventh means for coupling to said first channel a fifth directional audio input signal desired to be located midway of a pair of loudspeakers disposed around the listener to which said first and third directional audio input signals are desired to be coupled respectively; and

eighth means for coupling to said second channel a sixth directional audio input signal desired to be located midway of another pair of loudspeakers to which said second and fourth directional audio input signals are desired to be coupled respectively. I S. An encoder system acco rdi rig to claim [4 wherein said seventh means includes means for introducing a predetermined phase shift amount to said fifth directional audio input signal, and said eighth means includes means for introducing a predetermined phase shift amount to said sixth directional audio input signal.

16. An encoder system according to claim 8 wherein said first directional audio input signal is one which is desired to be coupled mainly to a first loudspeaker disposed at front-left side of the listening room, said second directional audio input signal to a loudspeaker disposed at front-right side, said third directional audio input signal to a loudspeaker at rear-left side, and said fourth directional audio input signal to a loudspeaker disposed at rear-right side.

17. An encoder system for use in a directional sound system wherein at least four directional audio input signals are respectively coupled to first and second chanysq n 599992.9 nnq j ssa s,at!!!V the first and second signals are decoded into at least four directional audio output signals which are coupled to at least four loudspeakers disposed around a listener in a listening room, said encoder system comprising:

first means for coupling a first directional audio input signal at a larger amplitude level to the first channel with a first phase shift amount; second means for coupling a second directional audio input signal at a larger amplitude level to the second channel substantially with said first phase shift amount;

third means for coupling a third directional audio input signal at a larger amplitude level to the first channel with a second phase shift amount;

fourth means for coupling a fourth directional audio input signal at a larger amplitude level to the second channel with a third phase shift amount;

fifth means for selectively coupling said first and second directional audio'input signals at smaller amplitude levels to the second and first channels substantially with said first phase shift amount, respectively;

sixth means for selectively coupling said third and fourth directional audio input signals at smaller amplitude levels to the second and first channels ,with said third and second phase shift amounts, re-

spectively;

seventh means for coupling to said first channel a fifth directional audio input signal desired to be located midway between a pair of ludspeakers disposed around the listener to which said first and third directional audio input signals are desired to be coupled respectively; and

eighth means for coupling to said second channel a sixth directional audio input signal desired to be located midway between another pair of loudspeakers to which said second and fourth directional audio input signals are desired to be coupled respectively;

said second and third phase shift amounts having differences of 45 to 135 and 45 to 135, respectively, with respect to said first phase shift amount.

18. An encoder system according to claim 37 wherein each of said fifth and sixth means includes a series connection of a manually operable switch and a resistor means.

19. An encoder system according to claim 18 wherein said resistor means includes variableresistor,

20. An encoder system according to claim 17 wherein said first to fourth means include first, second, third and fourth phase shifters, respectively, the phase shift characteristics of said third and fourth phase shifters having differences of 45 to 135 and 45 to 135, respectively, with respect to the phase shift characteristics of said first and second phase shifters.

21. An encoder system according to claim 20 wherein said first and 'second phase shifters have phase shift characteristics substantially equal to each other, and said third and fourth phase shifters have phase shift characteristics of about 90 and 90 differences with respect to those of said first and second phase shifters respectively.

22. An encoder system according to claim 17 wherein said seventh means includes means for introducing inw said fifth dir tipn lw adi in si n a 14 phase shift amount which substantially equals said first phase shift amount, and said eighth means includes means for introducing into said sixth directional audio input signal a phase shift amount which substantially equals said first phase shift amount.

23. An encoder system according to claim 17 wherein said first directional audio input signal is one which is desired to be coupled mainly to a first loudspeaker disposed at front-left side of the listening room. said second directional audio input signal to a loudspeaker disposed at front-right side, said third directional audio input signal to a loudspeaker at rear-left side, and said fourth directional audio input signal to a loudspeaker disposed at rear-right side.

24. For use with a directional sound system wherein, at an encoder side at least four directional audio input signals are utilized to produce first and second channel signals, and a first directional audio input signal at a larger amplitude level is coupled to a first channel with a first phase shift amount, a second directional audio input signal at a larger amplitude level is coupled to a second channel substantially with said first phase shift amount, a third input signal at a larger amplitude level is coupled to said first channel with a second phase shift amount, a fourth input signal at a larger amplitude level is coupled to said second channel with a third phase shift amount, said first and second input signals at smaller amplitude levels are coupled to said second and first channels substantially with said first phase shift amount respectively, and said third and fourth input signals at smaller amplitude levels are coupled to said second and first channels with said third and second phase shift amounts respectively, and, at a decoder side, said first and second channel signals are utilized to produce at least four directional audio output signals for coupling to at least four loudspeakers disposed around a listener in a listening room first, second, third and fourth audio output signals each including predominately corresponding one of said first, second, third and fourth audio input signals respectively, and being coupled to the respective loudspeakers through first, second, third and fourth output channels respectively, said decoder comprising:

first means for coupling said first channel signal at a larger amplitude level and said second channel signal at a smaller amplitude level to said first output channel with a fourth phase shift amount, which substantially corresponds to said first phase shift amount introduced into said first and second directional audio input signals respectively; 7

second means for coupling said second channel signal at a larger amplitude level and said first channel signal at a smaller amplitude level to said second output channel with said fourth phase shift amount;

third means for coupling said first channel signal at a larger amplitude level and said second channel signal at a smaller amplitude level to said third output channel with a fifth phase shift amount substantially corresponding to said third phase shift amount introduced into said fourth audio input signal and a sixth phase shift amount substantially corresponding to said second phase shift amount introduced into said third audio input signal respectively; and

fourth means for coupling said second channel signal at least Muss. .lEYilBPQ. sa d st chan el;

signal at a smaller amplitude level to said fourth output channel with said sixth and fifth phase shifts amounts respectively.

25. A decoder system according to claim 24 wherein said seventh and sixth phase shift amounts have differ- 5 ence of 45 to 135, and 45 to 135, respectively, with respect to said fourth phase shift amount.

26. A decoder system according to claim 25 wherein said fifth and sixth phase shift amounts have differences of substantially 90 and 90 with respect to said fourth phase shift amount respectively.

27. For use with a directional sound system wherein, at an encoder side at least four directional audio input signals are utilized to produce first and second channel signals, and a first directional audio input signal is coupled to a first channel with a first phase shift amount, a second directional audio input signal is coupled to a. second channel substantially with said first phase shift; amount, a third input signal is coupled to said first channel with a second phase shift amount, a fourth input signal signal is coupled to said second channel with a third phase shift amount, predetermined ampli-- tude levels of said first and second input signals are 25 coupled to said second and first channels substantially with said first phase shift amount respectively, and predetermined amplitude levels of said third and fourthinput signals are coupled to said second and first channels with said third and second phase shift amounts respectively, and, at a decoder side, said first and second channel signals are utilized to produce at least four directional audio output signals for coupling to at least four loudspeakers disposed around a listener in a listening room first, second, third and fourth audio output signals substantially corresponding to said first, second, third and fourth audio input signals respectively, and' being coupled to the respective loudspeakers through! first, second, third and fourth output channels respectively, said decoder comprising:

first ine ansiicluding said second channel signal with a predetermined amplitude level of said first channel signal, and a second phase shifter connected to the output of said coupling means;

third means including coupling means for coupling said first channel signal with substantially a 180 out-of-phase predetermined amplitude level of said second channel signal, and a third phase shifter connected to the output of said coupling means and having a phase shift characteristic of to 135 with respect to those of said first and second phase shifters; and

fourth means including coupling means for coupling said second channel signal with substantially a 180 out-of-phase predetermined amplitude level of said first channel signal, and a fourth phase shifter connected to the output of said coupling means and having a phase shift characteristic of 45 to 135 with respect to those of said first and second phase shifters.

28. An encoder system according to claim 27 wherein said third and fourth phase shifters have phase shift characteristics of substantially plus 90 and minus 90 differences with respect to those of said first and second phase shifters respectively.

29. A decoder system according to claim 27 further including means for varying a relative amplitude ratio between said first and second channel signals which are coupled to each of said first to fourth output channels.

"sfii'flii'coii'er system according 66min 27 wherein said first to fourth loudspeakers are respectively disposed in the listening room at front-left side, front-right side, rear-left side and rear-right side of the listener.

.3 5 -35 .nliw

'Pd--u' no STATES FATE "r oFFIcE (5/6 mm QERTEFKQAME QGQTION Patent No. 3,787,622 Dated January 22, 19741 R ouke ltoh d Tohloki lhdo Inveutofls) It is certified that error appeaxs in the above-identified patent and that said Lotto-rs Patout axe hereby ooz'rocted as shown below:

Column 1, line 64, after "2 insert is o Column 3, line 20, "q fil" ohould bo j and I "indicated" should be -=-lndi.cate-- line 23, after "shifted" insert --by--; line 37, "signals audio output" should be audio output signals; 1 line 39, "A should be AR line 5l,"differnot" should be --different-- line 56, after "difference" delete line 68, "signl" should be "signal".

Dolumn 4, line 13, "singals" should be -signals--;

line 24, after "and" insert --l9--; l1ne"44, fishifter 24" should be "shifter 14-"? Column 5, line 6 "root" should ho rear;

line 3 "contact" should be --electrode--; line 67, 'output" should be "input". Column 7 line 21, "otaining" should be "obtaining- Column 8, liue 2 before insert -RL-- line 6% "21" should be Column 9, line 12 "There," should be --Where,-'.

Column 10, line 7 (claim 2) dolooe "for (first occurrence) Ii-P641650? "fines-mum,,o ncE.

I CERTIFICATE-OF CORRECTION m m 3,787 622 mm Inventor) Ryosuke Itoh and Toshiakilshida Page 2 It is certified that error appears in the above-identified patent I and that said Letters Patent are hereby contacted as shown below:

Column ll, line 25 (cl?im 7%, "claim 10" should be --c aim ---1 line 64 (claim 8) 'levles" should be A v V v --levels--.

Column 12, line 16 (claim 9), "respecitvely" should read "respectively".

Column 13, 11M 30 (claim 17 "ludspeakers" should be --1oudspeakers--.

Column 15, lines 5 and 6 (claim 25), ,"difference" should be ---differencese t V H line 11 (claim 26), before "90" first occurrence,

Signed and sealed this 15th day of October; 1974.

(SEAL), Attest:

MCCOY M. GIBSON JR. 0'. MARSHALL DANN Attesting Officer Commissioner of Patents 

1. An encoding method for use in a directional sound system wherein at least first, second, third and fourth directional sound signals are respectively coupled to first and second channels to produce first and second channel signals, and the first and second channel signals are decoded into at least four directional audio output signals which are coupled to at least four loudspeakers disposed around a listener in a listening room, said encoding method comprising the steps of: combining said first sound signal at a larger amplitude level, said second sound signal at a smaller amplitude level, said third sound signal at a larger amplitude level, and said fourth sound signal at a smaller amplitude level in such a preselected phase relationship as said third sound signal and said fourth sound signal have substantially a plus 90* phase difference with respect to said first sound signal and said second sound signal, respectively, producing the first channel signal; and combining said first sound signal at a smaller amplitude level, said second sound signal at a larger amplitude level, said third sound signal at a smaller amplitude level, and said fourth sound signal at a larger amplitude level in such a preselected phase relationship as said third sound signal and said fourth signal have substantially a minus 90* phase difference with respect to said first sound signal and second sound signal, respectively, producing the second channel signal.
 2. A signal transmission system comprising: first means for obtaining multichannel signals by picking up sounds produced in a sound room; second means for connection to said first means for composing the multichannel signals into those of fewer channels by combining them; third meanS for for transmitting said signals of fewer channels; fourth means for connection to said third means for converting the signals of fewer channels to those of multichannels by combining them in preselected amplitude and phase relationships; and fifth means for connection to said fourth means for reproducing sounds from the multichannel signals of said fourth means; said first means comprising microphones MFL, MFR, MRL and MRR arranged on the front left and right sides and rear left and right sides of the sound source room so as to obtain four channel signals FL, FR, RL and RR respectively; said second means comprising an encoder having first, second, third and fourth phase shifters connected to receive said signals FL, FR, RL and RR, said first and fourth phase shifters being connected to receive said signals FL and FR respectively so as to shift the phase of said signals FL and FR by a reference angle, and said second phase shifter being connected to receive said signal RL so as to advance the phase of said signal RL within the range of from 45* to 135* relative to output signals of said first and fourth phase shifters, and said third phase shifter being connected to receive said signal RR so as to delay the phase of said signal RR within the range of from -45* to -135* relative to output signals of said first and fourth phase shifters, a first variable attenuator connected between both input terminals of said second and third phase shifters, a second variable attenuator connected between both output or both input terminals of said first and fourth phase shifters, said variable attenuators forming signals having amplitudes proportional to those of the signals supplied thereto with the proportional coefficient ranging within 0 to 1 including 0, a first adder connected to the output terminals of said first and second phase shifters, and a second adder connected between the output terminals of said third and fourth phase shifters, each of said adders producing one of said fewer channel signals as an output.
 3. A system according to claim 2 wherein the output signals of said first and fourth phase shifters are of the same phase, the output signal from said second phase shifter has its phase advanced 90* from those of said first and fourth phase shifters, and the output signal from said third phase shifter has its phase delayed 90* from those of said first and fourth phase shifters.
 4. A system according to claim 2 wherein said first means further comprises a microphone MCL disposed at the middle part of the microphones MFL and MRL placed at the front left side and rear left side of said sound source room respectively and another microphone MCR positioned at the middle of the microphones MFR and MRR located at the rear left side and rear right side of said sound source room respectively, thereby forming 6-channel signals FL, FR, RL, RR. CL and CR; and said encoder further includes a fifth phase shifter connected to receive said signal CL to shift the phase of an input by said reference angle, a sixth phase shifter connected to receive said signal CR to shift the phase of an input by said reference angle, a third adder connected to the output terminals of said fifth phase shifter and first adder to combine output signals therefrom, and a fourth adder connected to the output terminals of said sixth phase shifter and second adder to combine output signals therefrom, each of said third and fourth adders producing one of said fewer channel signals as an output.
 5. A system according to claim 4 wherein output signals from said fifth and sixth shifters have the same phase as those from first and fourth phase shifters.
 6. A system according to claim 4 wherein there is connected a first switch in series with said first variable attenuator disposed between terminals of said second and third phase shifters And a second switch in series with said second variable attenuator disposed between terminals of said first and fourth phase shifters.
 7. A system according to claim 10 wherein said fourth means comprises: first and second phase splitters supplied with said fewer channel signals from said third means; combining means connected to said phase splitters for combining output signals of said splitters; and first, second, third and fourth phase shifters connected to said combining means, the output signals from said first and fourth phase shifters being of the same phase, the output signal of said second phase shifter having its phase delayed 90* in phase with respect to those of said first and fourth phase shifters, and the output signal of said third phase shifter having its phase advanced 90* in phase with respect to those of said first and fourth phase shifters.
 8. An encoder system for use in a directional sound system wherein at least four directional audio input signals are respectively coupled to first and second channels to produce first and second channel signals, and the first and second channel signals are decoded into at least four directional audio output signals which are coupled to at least four loudspeakers disposed around a listener in a listening room, said encoder system comprising: first means for coupling a first directional audio input signal at a larger amplitude level to the first channel with a first phase shift amount; second means for coupling a second directional audio input signal at a larger amplitude level to the second channel substantially with said first phase shift amount; third means for coupling a third directional audio input signal at a larger amplitude level to the first channel with a second phase shift amount; fourth means for coupling a fourth directional audio input signal at a larger amplitude level to the second channel with a third phase shift amount; fifth means for coupling said first and second directional audio input signals at smaller amplitude levles to the second and first channels substantially with said first phase shift amount, respectively; and sixth means for coupling said third and fourth directional audio input signals at smaller amplitude levels to the second and first channels with said third and second phase shift amounts, respectively; said second and third phase shift amounts having differences of +45* to +135* and -45* to -135*, respectively, with respect to said first phase shift amount.
 9. An encoder system according to claim 8 wherein said first to fourth means include first, second, third and fourth phase shifters, respectively, the phase shifting characteristics of said first and second phase shifters being substantially equal to each other, and the phase shift characteristics of said third and fourth phase shifters having differences of +45* to +135* and -45* to -135*, respecitvely, with respect to the phase shift characteristics of said first and second phase shifters.
 10. An encoder system according to claim 8 wherein each of said fifth and sixth means includes resistor means.
 11. An encoder system according to claim 10 wherein each of said resistor means of said fifth and sixth means includes a variable resistor.
 12. An encoder system according to claim 10 wherein each of said fifth and sixth means includes a manually operable switch connected in series with said resistor means.
 13. An encoder system according to claim 9 wherein said third and fourth phase shifters have phase shift characteristics of about +90* and -90* differences with respect to those of said first and second phase shifters respectively.
 14. An encoder system according to claim 8 including: seventh means for coupling to said first channel a fifth directional audio input signal desired to be located midway of a pair of loudspeakers disposed around the listener to which said first and third directional audio input signals are desired to be coupled respectively; and eighth means for coupling to said second channel a sixth directional audio input signal desired to be located midway of another pair of loudspeakers to which said second and fourth directional audio input signals are desired to be coupled respectively.
 15. An encoder system according to claim 14 wherein said seventh means includes means for introducing a predetermined phase shift amount to said fifth directional audio input signal, and said eighth means includes means for introducing a predetermined phase shift amount to said sixth directional audio input signal.
 16. An encoder system according to claim 8 wherein said first directional audio input signal is one which is desired to be coupled mainly to a first loudspeaker disposed at front-left side of the listening room, said second directional audio input signal to a loudspeaker disposed at front-right side, said third directional audio input signal to a loudspeaker at rear-left side, and said fourth directional audio input signal to a loudspeaker disposed at rear-right side.
 17. An encoder system for use in a directional sound system wherein at least four directional audio input signals are respectively coupled to first and second channels to produce first and second channel signals, and the first and second signals are decoded into at least four directional audio output signals which are coupled to at least four loudspeakers disposed around a listener in a listening room, said encoder system comprising: first means for coupling a first directional audio input signal at a larger amplitude level to the first channel with a first phase shift amount; second means for coupling a second directional audio input signal at a larger amplitude level to the second channel substantially with said first phase shift amount; third means for coupling a third directional audio input signal at a larger amplitude level to the first channel with a second phase shift amount; fourth means for coupling a fourth directional audio input signal at a larger amplitude level to the second channel with a third phase shift amount; fifth means for selectively coupling said first and second directional audio input signals at smaller amplitude levels to the second and first channels substantially with said first phase shift amount, respectively; sixth means for selectively coupling said third and fourth directional audio input signals at smaller amplitude levels to the second and first channels with said third and second phase shift amounts, respectively; seventh means for coupling to said first channel a fifth directional audio input signal desired to be located midway between a pair of ludspeakers disposed around the listener to which said first and third directional audio input signals are desired to be coupled respectively; and eighth means for coupling to said second channel a sixth directional audio input signal desired to be located midway between another pair of loudspeakers to which said second and fourth directional audio input signals are desired to be coupled respectively; said second and third phase shift amounts having differences of + 45* to + 135* and - 45* to - 135*, respectively, with respect to said first phase shift amount.
 18. An encoder system according to claim 17 wherein each of said fifth and sixth means includes a series connection of a manually operable switch and a resistor means.
 19. An encoder system according to claim 18 wherein said resistor means includes a variable resistor.
 20. An encoder system according to claim 17 wherein said first to fourth means include first, second, third and fourth phase shifters, respectively, the phase shift characteristics of said third and fourth phase shifters having differences of + 45* to + 135* and - 45* to - 135*, respectively, with respect to the phase shift characteristics of said first and second phase shifters.
 21. An encoder system according to claim 20 wherein said first and second phase shifters have phase shift characteristics substantially equal to each other, and said third and fourth phase shifters have phase shift characteristics of about + 90* and - 90* differences with respect to those of said first and second phase shifters respectively.
 22. An encoder system according to claim 17 wherein said seventh means includes means for introducing into said fifth directional audio input signal a phase shift amount which substantially equals said first phase shift amount, and said eighth means includes means for introducing into said sixth directional audio input signal a phase shift amount which substantially equals said first phase shift amount.
 23. An encoder system according to claim 17 wherein said first directional audio input signal is one which is desired to be coupled mainly to a first loudspeaker disposed at front-left side of the listening room, said second directional audio input signal to a loudspeaker disposed at front-right side, said third directional audio input signal to a loudspeaker at rear-left side, and said fourth directional audio input signal to a loudspeaker disposed at rear-right side.
 24. For use with a directional sound system wherein, at an encoder side at least four directional audio input signals are utilized to produce first and second channel signals, and a first directional audio input signal at a larger amplitude level is coupled to a first channel with a first phase shift amount, a second directional audio input signal at a larger amplitude level is coupled to a second channel substantially with said first phase shift amount, a third input signal at a larger amplitude level is coupled to said first channel with a second phase shift amount, a fourth input signal at a larger amplitude level is coupled to said second channel with a third phase shift amount, said first and second input signals at smaller amplitude levels are coupled to said second and first channels substantially with said first phase shift amount respectively, and said third and fourth input signals at smaller amplitude levels are coupled to said second and first channels with said third and second phase shift amounts respectively, and, at a decoder side, said first and second channel signals are utilized to produce at least four directional audio output signals for coupling to at least four loudspeakers disposed around a listener in a listening room first, second, third and fourth audio output signals each including predominately corresponding one of said first, second, third and fourth audio input signals respectively, and being coupled to the respective loudspeakers through first, second, third and fourth output channels respectively, said decoder comprising: first means for coupling said first channel signal at a larger amplitude level and said second channel signal at a smaller amplitude level to said first output channel with a fourth phase shift amount, which substantially corresponds to said first phase shift amount introduced into said first and second directional audio input signals respectively; second means for coupling said second channel signal at a larger amplitude level and said first channel signal at a smaller amplitude level to said second output channel with said fourth phase shift amount; third means for coupling said first channel signal at a larger amplitude level and said second channel signal at a smaller amplitude level to said third output channel with a fifth phase shift amount substantially corresponding to said third phase shift amount introduced into said fourth audio input signal and a sixth phase shift amount substantially corresponding to said second phase shift amount introduced into said third audio input signal respectively; and fourth means for coupling said second channel signal at a larger amplitude level and said first channel signal at a smaller amplitude level to said fourth output channel with said sixth and fifth phase shifts amounts respectively.
 25. A decoder system according to claim 24 wherein said seventh and sixth phase shift amounts have difference of - 45* to - 135*, and + 45* to + 135*, respectively, with respect to said fourth phase shift amount.
 26. A decoder system according to claim 25 wherein said fifth and sixth phase shift amounts have differences of substantially 90* and + 90* with respect to said fourth phase shift amount respectively.
 27. For use with a directional sound system wherein, at an encoder side at least four directional audio input signals are utilized to produce first and second channel signals, and a first directional audio input signal is coupled to a first channel with a first phase shift amount, a second directional audio input signal is coupled to a second channel substantially with said first phase shift amount, a third input signal is coupled to said first channel with a second phase shift amount, a fourth input signal signal is coupled to said second channel with a third phase shift amount, predetermined amplitude levels of said first and second input signals are coupled to said second and first channels substantially with said first phase shift amount respectively, and predetermined amplitude levels of said third and fourth input signals are coupled to said second and first channels with said third and second phase shift amounts respectively, and, at a decoder side, said first and second channel signals are utilized to produce at least four directional audio output signals for coupling to at least four loudspeakers disposed around a listener in a listening room first, second, third and fourth audio output signals substantially corresponding to said first, second, third and fourth audio input signals respectively, and being coupled to the respective loudspeakers through first, second, third and fourth output channels respectively, said decoder comprising: first means including coupling means for coupling said first channel signal with a predetermined amplitude level of said second channel signal, and a first phase shifter connected to the output of said coupling means; second means including coupling means for coupling said second channel signal with a predetermined amplitude level of said first channel signal, and a second phase shifter connected to the output of said coupling means; third means including coupling means for coupling said first channel signal with substantially a 180* out-of-phase predetermined amplitude level of said second channel signal, and a third phase shifter connected to the output of said coupling means and having a phase shift characteristic of -45* to - 135* with respect to those of said first and second phase shifters; and fourth means including coupling means for coupling said second channel signal with substantially a 180* out-of-phase predetermined amplitude level of said first channel signal, and a fourth phase shifter connected to the output of said coupling means and having a phase shift characteristic of + 45* to + 135* with respect to those of said first and second phase shifters.
 28. An encoder system according to claim 27 wherein said third and fourth phase shifters have phase shift characteristics of substantially plus 90* and minus 90* differences with respect to those of said first and second phase shifters respectively.
 29. A decoder system according to claim 27 further including means for varying a relative amplitude ratio between said first and second channel signals which are coupled to each of said first to fourth output channels.
 30. A decoder system according to claim 27 wherein saId first to fourth loudspeakers are respectively disposed in the listening room at front-left side, front-right side, rear-left side and rear-right side of the listener. 